1. Technical Field
This application generally relates to data storage, and more particularly to techniques used with caching and a flash-based memory vault.
2. Description of Related Art
Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as those included in the data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more servers or host processors and provide storage services to each host processor. Multiple data storage systems from one or more different vendors may be connected and may provide common data storage for one or more host processors in a computer system.
A host processor may perform a variety of data processing tasks and operations using the data storage system. For example, a host processor may perform basic system I/O operations in connection with data requests, such as data read and write operations.
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units, disk drives, and disk interface units. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data in the device. In order to facilitate sharing of the data on the device, additional software on the data storage systems may also be used.
In connection with a write operation, the data storage system may utilize a variety of different techniques such as write-back caching. With write-back caching, the data storage system may temporarily cache data received from a host within its storage cache and destage the cached data at different times onto the physical disk drives. As known in the art, the cache used in the data storage system may be implemented using a fast, volatile memory, such as RAM (random access memory). The data storage system may utilize a backup or secondary power supply for use in connection with preventing loss of cached data in the event of a power failure. In the event of a power failure, the data storage system may utilize the backup power supply to provide power to the storage processor and physical data storage devices of the data storage system for a short period of time. During this period of time, the storage processor stores the data from its cache to a dedicated area on the storage devices that may be referred to as a “vault” so that the vault includes the cached data which has not yet been destaged onto the physical storage devices.
It should be noted that a data storage system may include multiple storage processors storing data to a same set of storage devices. Each of the storage processors may have its own cache so that cached data for the write operations, as well as possibly other cached data, may be mirrored in the caches of the storage processors. Multiple storage processors may be desirable for use in providing fault tolerance, higher throughput, and the like.